Helmets having a rigid or substantially rigid outer shell are used by sportsmen and workers involved in activities in which there is a risk of injury to the head.
The shape and design of protective helmets vary according to their intended use. In general, however, conventional protective helmets have a rigid or substantially rigid outer shell, cushioning means, such as foam padding and/or straps, and frequently a chin strap or similar device, to attach the helmet to the user's head. In such helmets the cushioning absorbs a major amount of the energy on impact with an object. While conventional protective helmets afford significant protection for the head of the user, such helmets are capable of improvement especially with respect to the amount of energy that may be absorbed by the shell of the helmet.
Protective helmets having two shells are known. For example, a protective helmet having interconnected internal and external shells is disclosed in U.S. Pat. No. 3,413,656 to G. Vogliano and D. Beckman, issued Dec. 3, 1968. A helmet having two shells and adapted for circulation of air between the shells for cooling is disclosed in Canadian Pat. No. 693,175 of R. F. Denton, issued Aug. 25, 1964.